Earthenware dishes and glaze therefor



Dec. 6, 1932. v McMASTER- 1,890,297

EARTHENWARE' DISHES AND GLAZE THEREFOR Filed Nov.. 7} 1 927 INVENTOR Patented Dec. 6, 1932 UNITED STATES PATENT OFFICE HARRY J'. MCMASTER, OF SEBRING, OHIO, ASSIGNOR OF ONE-FOURTH TO THE SEBRING POTTERY COMPANY, ONE-FOURTH TO THE LIMOGES CHINA COMPANY, ONE-FOURTH i TO THE CRESCENT CHINA COMPANY, ALL OF SEIBRING, OHIO, AND ONE-FOURTH To THE SALEM CHINA COMPANY, OF SALEM, OHIO, ALL CORPORATIONS OF OHIO EARTHENWARE'DISHES AND GLAZE THEREFOR- Application filed November 7, 1927. Serial No. 231,625.

This invention relates to the ceramic art and more particularly to the manufacture of earthen ware dishes and articles of table ware and to a glaze for such articles.

Earthen ware is recognized in the trade as being divided into two distinct classes and manufacturers of one class are ordinarily not manufacturers of the other class. The one class includes ornamental ware, such as vases and various ornamental objects. The second class consists of table ware, such as dishes.

In the manufacture of ornamental ware, glazes of variouscolors have been developed to add to the ornamental appearance of the ware. Such glazes, while highly ornamental, are not practical for use on table Ware because of the fact that they are not resistant to checking or crazing. In an article of ornamentation crazing and checking is not objectionable, and in some cases is purposely sought after to increase the ornamentation of the particular object. The development of checks or erazing in table ware is highly undesirable, however, because it makes the dishes unsightly. Also, due to the fact that crazing or checking consists of minute cracks in the glaze, grease and other substances can work into these cracks and be absorbed in the bisque body of the dish. This not only adds further to the unsightliness of the ware, but is highly unsanitary because it permits of the accumulation and development of bacteria on the dish.

Furthermore, colored glazes which have been developed for.ornamental ware, particularly yellow glazes, generally have been opaque. An opaque yellow glaze will not effectively show up applied decorations of certain colors. For instance, a yellow flower applied tovan opaque yellow glaze by a decalcomania process can not be made to show up to advantage. Furthermore, when other colors are applied to an opaque glaze by a decalcomania or other process and the colors burned onto the ware, the colors will be destroyed or blend with the opaque glaze in such a way as to change their coloror shade and spoil the effect which is sought. According to the practice heretofore generally used in giving an all-over color effect to earthen ware dishes, ithas first been necessary to apply the usual white glaze to the article. the glaze. After the glaze has been matured, the article is oiled and a powder is dusted over the oiled surface as smoothly as possible. This powder is of a nature such that upon burning it Willgive the desired color to the surface of the dish. After the powder has been dusted entirely over the surface of .the dish, the dish is again fired. If any ornamentation is to be used, such as a decalcomania ornamentation, the ornamentation must be applied after the dusting and second burning. After the decalcomania orother decoration has been applied, the article must then be burned a third time. Each burning operation entails a great deal of handling and a great deal of expense. With each operation a substantial percentage of dishes are broken and the process of coloring by dustin is therefore one which is very expensive. 1* ur- The article is then'burned to maturegood, or better advantage than it will appear on the ordinary white glaze. Furthermore, the glaze which I have developed is of such a nature that it has approximately the same coeflic-i-ent of expansion and contraction to thermal variations that the bisque body of the Ware has, so that it Will be highly resistant to crazing and checking.

Furthermore, the glaze which I have developed is applied directly to t-he'articlethe same way as the ordinary transparent white glaze, and dusting of coloring material in a previous glazing operation is not necessary. In order to make decorated, ware having yellow coloring over its entire surface, the dish can be made, according to my invention, with two firings, whereas with the dusting process it was necessary to burn the dish three times to secure a decorated article col-.

ored over its entire surface. The invention therefore results in a material saving in the cost of producing colored decorated dishes.

The invention maybe illustrated in connection with the accompanying drawing in which the figure represents an earthen ware dish, either porcelain or china, having my yellow glaze applied thereto and showing a decalcomania ornamentation thereon.

,In the drawing, the dish, which is designated 2, has a surface glaze 3 over its entire surface which is a brilliant transparent yellow glaze. This glaze is capable of receiving any type of ornamentation which can be used on ordinary white table ware, including color applied by brushes, rubber stamp impressions, gold stamping or bands, copper plate engravings, and decalcomania transfers in all colors. The glaze being transparent, the ornamentation may be applied directly to the bisque before it is glazed according to what is known as the under glaze process, or it may be applied to the glaze and then fired.

In the drawing we have illustrated the article as having a decalcomania decoration thereon consisting of flowers of various colors. This decoration is designated 4 and one of the flowers in the decoration, such as the flower 5, is shown as being yellow. The opaque yellow flower of the decoration contrasts with the transparent yellow .glaze. The other colors also show to good advantage, whereas a yellow flower on an opaque yellow laze would not look well, and the other colors would not show up to as good advantage. The burning of the colors into the opaque yellow glaze destroys the brightness of the colors, whereas the burning of the decoration into a transparent yellow glaze does not destroy the brilliance of the colors at all, and really enhances the appearance of the ware.

A transparent yellow glaze made in accordance with the present invention contains substantially the following analysis:

This analysis will give a relatively dark yellow color. For a bright pale yellow, the glaze has substantially the following composition:

The fritt used in the foregoing formulas consists of a fused mass which has been dumped in a molten condition into water and subsequently ground to a fine powder. The fritt contains the following analysis:

Formula Flint 29.67 Boric acid -1 22.03 Borax 5.46 Whiting 9.37 Spar 23.43

An ordinary white glaze contains substantlally the following analysis:

Formula4 Fritt (according to Formula 3) 30.42 Spar 22.19 Whiting 8.33 White lead 9.90 China clay 4.06 Flint 11.56 Zinc oxide 3.54

The yellow coloring is due primarily to the presence of the uranium salt, such as sodium uranate. In preparing the sodium uranate for use in a glaze it is made according to the following formula:

This is a dry mix' and is calcined in saggers in a glost kiln for several hours. This calcined mix is then mixed into 465 ints of white glaze (Formula 4) and withit is mixed 17 lbs. of red lead. To produce the light yellow transparent glaze, having the analysis of Formula 2, it is merely necessary to mix 4 pints of transparent white glaze (Formula 4) and one pint of dark yellow glaze (Formula 1). This produces five pints of the light yellow glaze (Formula 2).

While it is recognized that uranium oxide has been used in the manufacture of yellow glass ware, it was discovered that in order to produce asatisfactor yellov\-' glaze the quantity of uranium present must be below the quantity which a ceramic engineer would ordinarily expect to use. A ceramic engineer would expect the glaze to contain in excess of 8% of uranium salt, whereas I have discovered that where uranium is used in the expected proportions that a black non-transparent glaze entirel unsuited for commercial purposes results. or a transparent glaze of the character above given, I have found that the maximum amount of uranium salt should not exceed 8%. If a quantity in excess of 8% is used, some of the ware may be satisfactory, but other of the ware may have a very uneven dirty yellow appearance. Some of it would contain black or black spots and some of it would have a wavy brown and yellow appearance. By confinin the uranium content in the transparent g aze to 8% or below, dishes of commerciall uniform color can be secured. The uni ormity of color is important because of the fact that dinnerware is generally made in open stock lines. By this it is meant that replacement or additional ieces may be acquired from time to time y the purchaser. By reason of the color holding uniform it is possible to do this with the assurance that any piece will match the color of any other P1606. Even with the percentage as, low as 8%, and even lower, care must be taken in burning the ware that the atmosphere in the kiln is not a reducing one. The ware, in order to give uniformly satisfactory results, can not be burned in a reducing atmosphere. The percentage of sodium uranate in Formula 2 is the preferred content. This very small proportion gives a very bright even attractive yellow color that is not wavy or muddy looking and will show up the decora tions to very good advanta e. The proportions ma vary somewhat rom 1.56 of uranium in ormula 2, not, however, exceeding 2.00 or falling below 1.00. The uranium content may, however, go as low as .75 but as brilliant a color is not secured. Below .75 the glaze is extremely uncertain. Some of it may show yellow, some of it may be very pale yellow, and some of it may be white. The uranium content, therefore, ranges between .75 as a minimum and 8% as the approximate maximum, with the preferred range between 1 and 2%, and the most desirable quantity 1 or slightly in excess, i. e., 1.56. A transparent yellow glaze made in accordance with this invention is highly resistant to crazing or checking when applied to a good quality of bisque, such for instance, as that comprising the body of the better quality of porcelain dishes. Such porcelain has an analysis of approximately the following:

Formula 6 Per cent Flint 35 Spar 15 Wall clay 15 White kaoline 35 In making dishes according to our invention, the bisque is formed in the usual way and dried. It is immersed in the glaze just the same as dishes are ordinarily immersed in the ordinary colorless glaze. After being immersed, the Ware is burned in a glost kiln, care being taken that the atmosphere is oxidizing or neutral, rather than reducing. In burning the glaze matures as a smooth clear yellow transparent coating. To this glaze the decalcomania subject, or other decoration, is applied in the usual way and the article again fired in the decorating kiln. Upon removal of the article from the decorating kiln, the colors show up to full advantage and are not impaired in any way by reason of the fact that the glaze is yellow instead of clear.

It will be seen that with the present invention an all-over yellow coatin is secured with only one burning of the dis and this is the burning required for all earthen ware to mature the glaze. For decorated ware where the decoration is over the glaze, only two burnin s are necessary. As above pointed out, it as heretofore been necessary where an all-over color is desired to first glaze, then dust, and then burn again and if a decoration is needed still another burning is necessary. The invention therefore eliminates one burning with a subsequent reduction in handling and a consequent reduction in loss by breakage and a very considerable saving. Also, by confining the amount of uranium to the percentages herein indicated and burning the ware in a non-reducing atmosphere, the color is more even than can be secured with the dusting process.

Prior to the introduction of the present invention the use of a yellow glaze on any article, so far as I am aware, was very hard to secure and no yellow glaze was obtainable without requiring that the ware be burned twice. Furthermore, I am not aware that prior to the present invention any yellow glaze was developed which was highly resistant to crazing or which was transparent.

By roportionately increasing the amount of white lead in the laze according to Formulas 1 and 2, the red lead can be eliminated. However, the red lead is used as a matter of convenience. The proportion of red lead used in Formula 1 gives theraw wet laze a light salmon color, whereas without t e red lead it would be entirely white. The smaller percentage of red lead in Formula 2 makes the raw glaze a more pale salmon color but still a color which is readily distinguished from white. Where several tubs of the wet raw glaze are standing around the pottery, it is convenient to tell which is white glaze, which is pale yellow glaze, and which is dark ellow glaze by the distinction in color.

ithout the red lead, the light and dark yellowglaze would look the same as each other in the raw state and would look the same as the ordinary white glaze.

The glaze has a further important advantage in that it matures uniformly notwithstanding the varying temperature and atmospheric conditions of the kiln. My early experiments showed that some pieces of ware in certain parts of the kiln would be one color while other pieces were of an entirely different shade of yellow. Most of the ware would not be salable at all due to the fact that a single piece would contain several different shades and the color would frequently be blotched and uneven. The colors would range from a black to a dirty green and browns to various shades of yellow, and from the contents of an entire kiln only a few pieces which would match in color would be obtained. This made it necessary to sort through the entire contents of the kiln, select several different shades, and classify the" ware according to the different shades. The great proportion of the ware would not be salable at all and the pieces that were salable demanded an excessively high price. The glaze as developed produces ware of even uniform color, the pieces taken from the kiln matching uniformly with the color being uniformly spread over each piece without blotches and without waves.

lVhile I have described the invention in detail, it will be understood that this is merely illustrative of the invention and that various changes and modifications may be made therein within the contemplation of my invention and under the scope of the following claims.

I claim:

1. In the manufacture of yellow glaze dishes of uniform color intensity, the steps which comprise calcining sodium uranate with china clay and flint, adding the calcined mass to a. transparent white glaze composition in such proportion that the quantity of uranium salt in the resulting mixture shall be approximately between 1 to 3 percent of the total mass, dipping an unglazed dish into the mixture and thereafter firing the ware in a non-reducing atmosphere.

2. The method of making yellow glaze table ware in which the articles of table ware have a uniform yellow color and wherein the articles all match in color, which comprises calcining sodium uranate with china clay and flint, adding the calcined mass to a trans-- parent white glaze composition in such proportion that the quantity of uranium salt in the resulting mixture shall be approximately between 1 and 3 percent of the total mass, dipping the articles to be glazed into the resulting mix, and firing them.

3. In the manufacture of dishes having a transparent yellow glaze, the steps which comprise calcining a uranium salt with china clay andv flint, adding the calcined mass to a transparent white glaze composition conmy hand.

HARRY J. MGMASTER. I, 

